In a wavelength-division multiplexing (WDM) optical system, multiple light signals at different wavelengths may be joined and transmitted along a waveguide to increase transmission capacity for the system. However, the multiple light signals may not share the same destination in the system, and some selected light signals at particular wavelengths may be switched to another waveguide with a different destination. Thus, it may be useful to enable a selection of light signals at particular wavelengths for switching.